1. Field of the Invention:
The present invention relates to a combustion chamber of a sub-chamber type internal combustion engine.
2. Description of the Prior Art:
A combustion chamber of sub-chamber type internal combustion engine in the prior art is illustrated in FIG. 17. In this figure, a subsidiary combustion chamber 2 is formed in a cylinder head 4. As to the configuration of the subsidiary combustion chamber 2, a hemispherical upper portion combined with a frusto-conical lower portion or a circular-pillar-shaped lower portion is known, and in FIG. 17 is shown the configuration including a frusto-conical lower portion. At the subsidiary combustion chamber 2 is disposed a fuel injection valve 5 and, if necessary, a glow plug for preheating the interior of the subsidiary combustion chamber 2 upon starting of the engine. The subsidiary combustion chamber is communicated through a sub-chamber port 3 with a main combustion chamber 1 that is formed of a top surface of a piston 7, a cylinder 8 and a bottom surface of cylinder head 4. The cross-sectional area of the path through sub-chamber port 3 is constant.
In the combustion chamber of the above-described sub-chamber type internal combustion engine of the prior art, air in the main combustion chamber 11 is compressed by the piston 7 during a compression stroke upon operation of the engine, then it flows into the subsidiary combustion chamber 2 through sub-chamber port 3, and thereby a swirling air flow (S) is produced. If fuel is injected from fuel injection valve 5 along the directed of the swirling flow (S), the fuel will revolve within the subsidiary combustion chamber 2 jointly with the swirling flow (S), thus mixing of the fuel and air is effected, and the mixture is ignited and burnt. Combustion gas and unburnt fuel within the subsidiary combustion chamber 2 are ejected through the sub-chamber port 3 into the main combustion chamber and work the piston, and at the same time mixing with air in the main combustion chamber 1 and combustion are effected. In other words, the jet flow emanating from the subsidiary combustion chamber 2 will reach the cylinder wall on the opposite side of the subsidiary combustion chamber 2 with respect to the cylinder center line B--B, will collide against that wall surface, and after such collision it will be dispersed along the wall surface of the cylinder 8.
In the above-described combustion chamber of a sub-chamber type internal combustion engine of the prior art, in order to improve fuel consumption as well as starting performance upon partial loading of the engine, it is important to increase the cross-sectional area of the path through the sub-chamber port 3 to attempt to reduce thermal loss and throttling loss at the sub-chamber port. If the cross-sectional area of the sub-chamber port 3 is increased for that purpose, then upon heavy loading, the flow speed of the jet into the subsidiary combustion chamber 2 is reduced. Hence the swirling low speed and further the jet flow speed within the main combustion chamber 1 are reduced, so that mixing and combustion of fuel and air within the main and subsidiary combustion chambers is reduced, and fuel consumption as well as smoke density are deteriorated. On the other hand, if the path cross-section area of the sub-chamber port 3 is decreased in order to promote combustion and improve fuel consumption and smoke density, then the thermal loss and throttling loss at the sub-chamber port upon partial loading or upon starting are increased, as described previously, and thus fuel consumption as well as starting performance are deteriorated.